It's well known that you can't copyright a recipe, so it's natural that the ethics of trading them on the information superhighway has become an issue among food bloggers. From the Copyright Office:
How do I protect my recipe?
A mere listing of ingredients is not protected under copyright law. However, where a recipe or formula is accompanied by substantial literary expression in the form of an explanation or directions, or when there is a collection of recipes as in a cookbook, there may be a basis for copyright protection. Note that if you have secret ingredients to a recipe that you do not wish to be revealed, you should not submit your recipe for registration, because applications and deposit copies are public records.
WaPo published a lengthy discussion back in January and now the bloggers are unconsciously creating their own code of ethics around this issue. I find it quite respectful.
Tigers and Strawberries has an excellent post addressing several aspects of attribution.
Megnut feels better after reading the WaPo article.
Accidental Hedonist lays down the law.